Proboscis Monkey (Nasalis larvatus)
The primates are represented in Borneo by six families including the Hominidae, the family of Man. All primates have hands and feet which can grasp, digits generally with nails rather than claws, and both eyes on the front of the face. The Lorisidae and Tarsiidae are strictly nocturnal. The monkeys (family Cercopithecidae) and apes (families Hylobatidae and Pongidae) are diurnal and, along with tree squirrels and treeshrews, are the only mammals active in trees during the daytime.
Monkeys in Borneo are represented by two distinct groups: the langurs or leaf monkeys and the Proboscis Monkeys (subfamily Colobinae) and the macaques (subfamily Cercopithecidae). The colobines are mainly arboreal, have a long tail, lack cheek pouches and have a large, sacculated stomach which permits breakdown of leafy material into digestible substances and helps detoxify poisonous leaves. The macaques are partly terrestrial, with a short or long tail, cheek pouches for temporary storage of food and a simple stomach capable of breaking down only a limited amount of leafy material.
Measurements: (adult males) HB 555-651, T 674-745, HF 210-225, Wt 12-23 kg (4 specimens); (adult females) HB 550-555, T 620-570, HF 190-193 (2 specimens), Wt about 10 kg.
Identification: Upperparts generally dull, pale greyish-yellow to red-brown, darker on the upper back, with a reddish-brown cap on top of the head; underparts paler. Tail and rump whitish, especially in adult males. Adult males have a pale collar around the front and sides of the neck and a much larger nose than females. When sitting in a tree, tail usually hangs vertically downwards. Infants have a dark blue face. Makes a wide range of distinctive noises, including honks, groans, squeals and loud roars.
Similar species: other monkeys are smaller and have dark tails.
Ecology and Habitat: Diurnal, but most active early morning and late afternoon when leaving or moving to sleeping sites, usually on a river bank. Mostly arboreal, but will swim across rivers or walk across open areas to reach isolated patches of forest. Social structure apparently flexible, with small parties often joining into temporary large groups. Diet includes leaves, fruits and shoots. In eastern Sabah, most often found in mangrove forests, mixed mangrove and nipah and in river edge forests. Seldom encountered in pure stands of nipah, Casuarina, coastal heath or swamp forests. In Sarawak and Kalimantan, may be more common in riverine and peat swamp forests. Solitary males occasionally seen in other forest types many kilometres from any mangrove or large river. Function of large nose unknown.
Distribution: This species is restricted to Borneo and a few inshore islands, notably those at the mouth of S. Brunei and on P. Sebatik off the Sabah/East Kalimantan border. Usually found near large water courses.